This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-114872, filed Apr. 22, 1999; and No. 11-367582, filed Dec. 24, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an oil application roller for use in a fixing unit of an electrophotographic image-forming apparatus, such as a copying machine, facsimile, or laser beam printer.
An electrophotographic image-forming apparatus basically comprises an electrostatic latent image-forming unit for forming an electrostatic latent image on a photosensitive drum by exposing the photosensitive drum in accordance with the predetermined image information. A developing unit is provided for forming a toner image (visible image) corresponding to the electrostatic latent image by supplying and attaching toner from a developing roller onto the electrostatic latent image formed on the photosensitive drum. A transferring unit transfers the toner image formed on the photosensitive drum on recording paper, and a fixing unit firmly fixes the transferred toner image on the recording paper.
At the fixing unit, energy of pressure and heat is applied through a fixing member, such as a fixing roller or a fixing belt, to the unfixed toner image held on the recording paper. The toner particles of the toner image become semi-melted and permeated into the recording paper as the energy is applied, thus completing the fixing process. Since the toner particles are adhesive during the fixing process, an offset-preventing oil (for example, silicone oil) is applied from an oil application roller to a surface of the fixing member. Such an oil application roller is desired to be capable of applying a very small amount (usually, 0.5 to 2 mg on an A4 sheet of paper) of an offset-preventing oil onto the fixing member steadily for a long period of time.
For example, an oil application roller is known in the art which comprises a core shaft with a sheet of non-woven paper, such as aramid paper, wound thereon. The non-woven paper is impregnated with a silicone oil. Another sheet of non-woven paper is wound to cover the oil-impregnated paper. However, it has been found that an oil application roller of this type is not able to stably form a nip required for the oil application, between the oil application roller and the fixing member, under a small load. As a result, the amount of oil applied becomes nonuniform with time. The uppermost non-woven paper has a poor releaseability and clogs up due to contamination by the toner. Thus, the oil application roller of the type mentioned above cannot provide a constant oil amount applied.
In addition, an oil application roller is also known which comprises a core shaft with a layer of a silicone sponge placed thereon. The sponge layer is impregnated with a silicone oil. A non-woven fabric such as aramid felt is provided to cover the oil-impregnated silicone sponge layer. However, an oil application roller of this type cannot supply the oil onto the fixing member for a long period of time. This is because, when impregnating the silicone sponge with the silicone oil, the silicone sponge becomes swelled, resulting in an insufficient amount of oil impregnated. Further, it has been found that, as the oil is applied, the surface hardness of this oil application roller increases, with the result that the width of a nip between the oil application roller and the fixing member becomes smaller, leading to the reduction in the amount of oil applied. In addition, the uppermost non-woven fabric has the same drawback as in the above-noted prior art oil application roller.
Thus, the prior art oil application rollers cannot steadily apply a very small amount of an offset-preventing oil for a long period of time.
It is, therefore, an object of the present invention to provide an oil application roller which can steadily apply a very small amount of an offset-preventing oil for a long period of time.
The present inventors have studied on oil application rollers in an attempt to achieve the above-noted object. As a result, the present inventors have found that the above-noted object can be achieved by constituting an oil retention/supply layer, which retains an offset-preventing oil therein and supplies the oil therefrom, by a porous elastic material which exhibits no substantial swelling against the offset-preventing oil used. The oil retention/supply layer is impregnated with an offset-preventing oil together with a curable rubber, which is then cured. The present invention is based on these findings.
Thus, the present invention provides an oil application roller comprising a core shaft, and an oil retention/supply layer formed to cover the outer peripheral surface of the core shaft and comprising a porous elastic material which exhibits no substantial swelling against an offset-preventing oil used, the oil retention/supply layer being impregnated with a mixture containing an offset-preventing oil and a curable oil-retention material, with the curable oil-retention material being cured.
According to the present invention, there is also provided an oil application roller comprising a core shaft, and an oil retention/supply layer formed to cover the outer peripheral surface of the core shaft and comprising a porous melamine resin elastic material, the oil retention/supply layer being impregnated with a mixture containing an offset-preventing oil and a curable oil-retention material, with the curable oil-retention material being cured.
According to the present invention, there is further provided an oil application roller comprising, as an uppermost layer, an oil retention/supply layer comprising a porous elastic material which exhibits no substantial swelling against an offset-preventing oil used, the oil retention/supply layer containing a mixture containing an offset-preventing oil and a curable oil-retention material such that an amount of the oil supplied from the oil retention/supply layer may be substantially constant, with the curable oil-retention material being cured.
In the present invention, the curable oil-retention material may be a curable or vulcanizable rubber. It is further preferred that the offset-preventing oil comprises an silicone oil, and the curable oil-retention material comprises a two-pack or one-pack curable or vulcanizable silicone rubber.
Further, in the present invention, it is preferred that the offset-preventing oil and the curable oil-retention material are impregnated at an initial weight ratio of from about 1:1 to 20:1.
In a preferred embodiment of the present invention, the oil retention/supply layer has, on its peripheral surface, a surface layer which at least fills pores present at the surface thereof resulting from the porousness of the oil retention/supply layer. The surface layer may comprise a mixture containing an offset-preventing oil and a curable oil-retention material.
Further, an oil application roller according to the present invention can exhibit a surface glossiness of 1% or more. Particularly, when the oil application roller has the surface layer as described above, the roller may exhibit a surface glossiness of 3% or more.
An oil application roller according to the present invention preferably has a regular crown shape.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.